1. Field of the Invention
The present invention relates to a VoIP (Voice over Internet Protocol) network system of a peer-to-peer type in which host terminals transmit or receive packets by multicast communication to one another without a server, and a method of constructing such a VoIP network system.
2. Description of the Background Art
Conventionally, VoIP network systems are constructed without a server. There is known a peer-to-peer network in which terminals communicate unicast packets to directly each other.
Japanese patent laid-open publication No. 2003-134 discloses an IP (Internet Protocol) telephone set that utilizes VoIP to make conversation. If the IP telephone set receives from an operator a call originating request accompanied by the telephone number of a party to be called, the IP telephone set sends a multicast packet containing that telephone number to a local area network (LAN), obtains a response packet to the multicast packet, and sets the source IP address of the response packet into the IP address of the called party.
In addition, U.S. patent application publication No. 2004/0252691 A1 to Hori et al., discloses a VoIP system. In the VoIP system, in response to a request from a client, a VoIP server transmits multicast packets to other clients. At this time, the VoIP server determines whether or not the other clients are able to receive multicast packets. To clients determined to be capable of receiving multicast packets, data is transmitted in the form of multicast packets. To clients determined to be incapable of receiving multicast packets, data is transmitted in the form of unicast packets.
However, in the conventional VoIP network systems, for example, if a certain host terminal sends its own address information to other respective host terminals by unicast packet communication on a one-to-one terminal basis, the former host terminal has to transmit a number of packets that corresponds in number to the destination host terminals. Particularly, in the case where packets are transmitted through routers to other host terminals outside a closed network, the number of packets to be transmitted is increasing explosively, so that network load is increasing exponentially and packet traffic on the network is getting heavier and heavier.